1. Field of the Invention
The present invention relates to a gas compression apparatus, applicable effectively to a screw pump, in which the lubricant oil cannot be mixed with the discharge gas.
2. Description of the Related Art
A gas compression apparatus comprising a fixed member and rotative members for compressing and discharging a gas includes bearings for supporting the rotative members rotatably, which bearings are normally supplied with a lubricant oil from a lubricant space containing the lubricant oil.
In a prior art, an intermediate pressure chamber communicating with a compression chamber in the compression process is formed in a seal section on a discharge side in order to suppress the reduction in volume efficiency due to the leakage of the lubricant oil from the compression chamber to the lubricant space, as disclosed in Japanese Unexamined Patent Publication No. 2001-182680.
In another prior art, as disclosed in Japanese Unexamined Patent Publication No. 5-312165, a gear chamber and a compression chamber communicate with each other through a pressure balance chamber. In the case where the internal pressure of the gear chamber increases beyond the internal pressure of the compression chamber, a check valve is opened to release the internal pressure of the gear chamber into the compression chamber. In this way, the pressure difference between the gear chamber and the compression chamber is reduced to thereby reduce the friction force generated by a seal member for a rotor shaft arranged through a partitioning wall between the gear chamber and the compression chamber.
A gap between the shaft, arranged through a partitioning wall between the lubricant space and the compression chamber, and the partitioning wall is hermetically sealed by the seal member, as described above. In view of the fact that the shaft rotates while in contact with the seal member, however, the lubricant space and the compression chamber undesirably communicate with each other through a minuscule gap generated at the contact surfaces of the shaft and the seal member. It is therefore difficult to completely shut off the lubricant space and the compression chamber from each other.
As long as the gas compression apparatus is in operation, however, the internal pressure of the compression chamber is higher than the internal pressure of the lubricant space. Therefore, the amount of the lubricant oil leaking into the compression chamber from the lubricant space through the minuscule gap generated at the contact surfaces of the shaft and the seal member is negligibly small. Thus, the possibility is very low that the lubricant oil mixes with the discharge air. As the internal pressure of the compression chamber is higher than the internal pressure of the lubricant space, however, the high-pressure gas in the compression chamber leaks into the lubricant space through the minuscule gap generated at the contact surfaces of the shaft and the seal member.
In the case where the operation of the gas compression apparatus is stopped with a high internal pressure of the lubricant space, the internal pressure of the lubricant space increases to beyond the internal pressure of the compression chamber unlike in the case where the gas compression apparatus is in operation. As a result, the lubricant oil in the lubricant space is liable to leak out into the compression chamber through the minuscule gap generated at the contact surfaces of the shaft and the seal member.
Once the lubricant oil comes to stay in the compression chamber while the gas compression apparatus is out of operation, therefore, the lubricant oil staying in the compression chamber is discharged out of the gas compression apparatus together with the discharge gas when the operation of the gas compression apparatus is restarted.